Process for making polymers having nanostructures incorporated into the matrix of the polymer

ABSTRACT

The present invention is directed toward a method for making a polymer that has nanostructures incorporated into the matrix of the polymer. The method of the invention involves the following steps: mixing a precursor solution for the polymer with a precursor for the nanostructures to form a mixture; forming nanostructures in the mixture from the precursor of the nanostructures; and forming a polymer from the precursor solution of the polymer so that the nanostructures are incorporated into the polymer matrix.

FIELD OF INVENTION

The present invention relates to a process for making polymers havingnanostructures incorporated into the matrix of the polymer.

BACKGROUND OF THE INVENTION

Products such as aerospace and automotive transparencies, opticallenses, coating compositions, fiberglass surface modifiers, etc. aremade of various polymers. In an attempt to make better products,scientists and engineers have tried to optimize the performanceproperties of the polymers used to make the products. Various techniqueshave been proposed for optimizing the performance properties ofpolymers.

For example, scientists and engineers have attempted to incorporatenanostructures into polymer matrices to modify the performanceproperties of a polymer. Because nanostructures have significantlydifferent physical properties from corresponding bulk material and thepolymer matrix, incorporating the nanostructures changes the performanceproperties of the polymer. Nanostructures have been incorporated intopolymer matrices to improve the thermal stability of polymers and todecrease the chemical activity of polymers.

Conventionally, nanostructures have been incorporated into the matrix ofa polymer by taking pre-made nanostructures and dispersing them into thepolymer solution. Typically, the dispersing step includes several othersteps such as modifying the surface, mixing, stirring, heating, milling,etc. The conventional process is inefficient due to the multiple stepsinvolved and tends to produce polymers in which the nanostructuresagglomerate. When nanostructures agglomerate in the polymer, thenanostructures can effectively become regular sized particles and thedesired effect of incorporating the nanostructures is reduced.

The present invention provides an improved process for making a polymerhaving nanostructures incorporated into the matrix of the polymer.Polymers produced according to the present invention undergo reducednanostructure agglomeration.

SUMMARY OF THE INVENTION

In a non-limiting embodiment, the present invention is a method formaking a polymer that has nanostructures incorporated into the matrix ofthe polymer comprising: mixing a precursor solution for the polymer witha precursor for the nanostructures to form a mixture; formingnanostructures in the matrix of the polymer from the precursor of thenanostructures; and forming a polymer from the precursor solution of thepolymer.

In another non-limiting embodiment of the invention, the presentinvention is a method for making a polymer that has nanostructuresincorporated into the matrix of the polymer comprising: mixing aprecursor solution for the polymer comprising polyvinyl alcohol with aprecursor for the nanostructures selected from monobutyl tintri-chloride and indium acetate to form a mixture; formingnanostructures in the matrix of the polymer from the precursor of thenanostructures; and forming a polymer from the precursor solution of thepolymer.

In yet another embodiment, the present invention is a method for makinga polymer that has nanostructures incorporated into the matrix of thepolymer comprising: mixing a precursor solution for poly [bis(diethyleneglycol)diallylcarbonate], with a precursor for the nanostructurescomprising titanium iso-propoxide to form a mixture; formingnanostructures in the matrix of the polymer from the precursor of thenanostructures; and forming a polymer from the precursor solution of thepolymer.

In a further embodiment of the invention, the present invention is amethod for making a polymer that has nanostructures incorporated intothe matrix of the polymer comprising: mixing a precursor solution fortrimethylol propane, methylene bis(4-cyclohexylisocyanate),thiodiethanol with a precursor for the nanostructures selected frommonobutyl tin tri-chloride and indium acetate to form a mixture; formingnanostructures in the matrix of the polymer from the precursor of thenanostructures; and forming a polymer from the precursor solution of thepolymer.

DESCRIPTION OF THE INVENTION

As used herein, all numbers expressing dimensions, physicalcharacteristics, processing parameters, quantities of ingredients,reaction conditions, and the like, used in the specification and claimsare to be understood as being modified in all instances by the term“about”. Accordingly, unless indicated to the contrary, the numericalvalues set forth in the following specification and claims may varydepending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical value should at least be construed in light of the numberof reported significant digits and by applying ordinary roundingtechniques. Moreover, all ranges disclosed herein are to be understoodto encompass the beginning and ending range values and any and allsubranges subsumed therein. For example, a stated range of “1 to 10”.should be considered to include any and all subranges between (andinclusive of) the minimum value of 1 and the maximum value of 10; thatis, all subranges beginning with a minimum value of 1 or more and endingwith a maximum value of 10 or less, e.g., 1.0 to 3.8, 6.6 to 9.7 and 5.5to 10.

As used herein, the term “nanostructure” refers to a three dimensionalobject wherein the length of the longest dimension ranges from 1 nm to1000 nm, for example, from 1 nm to 500 nm, or from 1 nm to 100 nm, orfrom 1 to 40 nm.

As used herein, the phrase “precursor solution for the polymer” refersto any material that can be used as a starting material to form thepolymer.

As used herein, the phrase “precursor for the nanostructures” refers toany material that can be used as a starting material to form thenanostructures.

In a non-limiting embodiment, the present invention is a process formaking a polymer having nanostructures incorporated into the matrix ofthe polymer. According to the present invention, the first step in theprocess involves mixing a precursor solution for a polymer and aprecursor for the nanostructures that are to be incorporated into thematrix of the polymer to form a mixture. The precursor solution for thepolymer does not include any nanostructures initially. The exactprecursor solution for the polymer used in the present invention dependson the polymer that is desired in the end product.

For example, if the desired end product is a polyvinyl acetal resin suchas polyvinyl butyl (PVB), suitable precursors for the polymer include,but are not limited to, polyvinyl alcohol (PVA).

As another example, if the desired end product is poly [bis(diethyleneglycol)diallylcarbonate], suitable precursors for the polymer include,but are not limited to, bis(diethylene glycol)diallylcarbonate monomer.

As yet another example, if the desired end product is an aliphaticpolyurethane, suitable precursors for the polymer include, but are notlimited to, 1,4-butanediol, trimethylol propane, andbis(4-isocyanotocyclohexyl)methane which is commercially available asDesmodur® W from Bayer Material Science in Pittsburgh, Pa., andthiodiethanol.

In a non-limiting embodiment of the invention, a solvent such as water,ethanol, iso-propanol, butanol, etc. is added to the mixture.

According to the present invention, the second step in the processinvolves forming the nanostructures from the precursor of thenanostructures in the matrix of the polymer. The nanostructures areformed while the viscosity of the polymer is low so that thenanostructures can incorporate themselves into the matrix of thepolymer. The formation of the nanostructures can be initiated usingvarious techniques. In a non-limiting embodiment of the invention, thenanostructures are formed by adjusting the pH of the mixture. An acid orbase, such as ammonia, can be used to adjust the pH of the solution.Depending on the exact precursor solution of the polymer and the exactprecursor for the nanostructures, there is an optimum pH range in whichthe nanostructures will form. One of ordinary skill in the art will knowwhat the optimum pH range is based on both precursors.

In another non-limiting embodiment, the mixture can be heated toinitiate the formation of the nanoparticles. The mixture can be heatedto any temperature provided the mixture is not be heated to atemperature above that at which the precursor solution would break down.For example, a precursor solution comprising PVA cannot be heated above200° C. because that is the temperature at which PVA begins todecompose. Similarly to the pH range, the optimum temperature range atwhich the particles will form depends on the exact precursor solution ofthe polymer and the exact precursor for the nanostructures. One ofordinary skill in the art will know what the optimum temperature rangeis based on both precursors. Generally, the higher the temperature towhich the mixture is heated and/or the longer the mixture is heated, thelarger the size of the nanostructures that will be formed.

In yet another non-limiting embodiment of the invention, forming thenanostructures is accomplished by heating the mixture after the pH ofthe mixture is adjusted. In a further non-limiting embodiment of theinvention, forming the nanostructures is accomplished by heating themixture and then adjusting the pH of the mixture.

In various other non-limiting embodiments of the invention, thenanostructures can be formed by using one or more of the following:increasing the pressure on the mixture; by changing the concentration ofthe precursor solution for the polymer; by using an initiator fornanostructure formation; and by seeding (adding no greater than 5% ofthe desired nanostructure material based on the projected weight of theformed nanostructures as is well known in the art).

The formed nanostructures are charged species. If the pH of the solutionwas adjusted to cause the formation of the nanostructures, the charge isa result of the pH adjustment. If no pH adjustment was performed duringthe nanostructure formation step, a polymeric stabilizer such as, butnot limited to, sodium polymethacrylate in water and ammoniumpolymethacrylate in water, which are both commercially available asDarvan® 7 and as Darvan® C, respectively, from R.T. Vanderbilt Company,Inc. in Norwalk, Conn. can be added to the solution to create thecharge.

According to the present invention, the third step involves forming thepolymer from a mixture including the precursor solution of the polymer.The formation of the polymer can be initiated using various techniques.One of ordinary skill in the art will know what technique to use basedon the precursor solution of the polymer and the precursor for thenanostructures.

In a non-limiting embodiment of the present invention, the second andthird steps described above are switched.

The method of making polymers having nanostructures incorporated intothe matrix of the polymer according to the present invention is referredto as “in-situ” process. This means the nanostructures are formed duringthe same process that produces the polymer as opposed to pre-formednanostructures being dispersed into a polymer solution.

During the method of the present invention, ions (cations and/or anions)can form in the mixture. The formed ions and other process variablessuch as the pressure of the system in which the mixture is held, canaffect the final polymer. For example, the amount of nanostructureformation and the morphology of the nanostructures will vary dependingon the types and amount of ions present in the solution.

In the polymer matrix, the nanostructures typically continually approachone another and collide because they possess kinetic energy. Undernormal circumstances, some of the nanostructures would become boundtogether and agglomerate due to various forces such as Van der Waalsforces. As discussed above, agglomeration is not desirable because thenanostructures can effectively become regular sized particles and thedesired effect of incorporating the nanostructures is reduced.

However, the method of the present invention produces polymers havingnanostructures in the matrix of the polymer that do not agglomerate tothe extent the performance of the polymer is compromised. Thenanostructures do not agglomerate because they are stabilized. Thestabilization occurs via three mechanisms: (1) electrostaticstabilization, (2) steric stabilization and (3) a combination ofelectrostatic stabilization and steric stabilization.

Because the nanostructures in the polymer matrix are similarly chargedspecies, they repel each other. This prevents the nanostructures fromcoming so close together that they agglomerate. This phenomenon isreferred to as electrostatic stabilization.

Because the nanostructures are surrounded by polymer precursor solutionwhen they are formed, the nanostructures lose a degree of freedom whichthey would otherwise possess as the nanostructures approach each other.This loss of freedom is expressed, in thermodynamic terms, as areduction in entropy, which provides the necessary barrier to hinderagglomeration. This phenomenon is referred to as steric stabilization.The same principle applies when the method of the invention involvesforming the polymer before forming the nanostructures.

The polymer formed according to the present invention can have thefollowing properties. The concentration of the nanostructures in thepolymer matrix can range from 0.1% to 90%, for example from 3% to 85% orfrom 15% to 80% based on volume. The nanostructures in the polymermatrix can have the following shapes: spherical, polyhedral-like cubic,triangular, pentagonal, diamond shaped, needle shaped, rod shaped, discshaped etc. The nanostructures in the polymer matrix can have an aspectratio of 1:1 to 1:1,000, for example 1:1 to 1:100.

The nanostructures in the polymer matrix can have a longest dimensionranging from 1 nm to 1,000 nm, for example, 1 nm to 500 nm, or 1 nm to100 nm, or 1 nm to 40 nm. If the nanostructures agglomerate, the size ofthe nanostructures could effectively become so large that the desiredperformance of the polymer is compromised. This is the problem withpolymers having preformed nanostructures incorporated into the polymermatrix as discussed earlier.

The polymers formed according to the present invention can be used in anumber of applications. The formation of specific polymers havingspecific nanostructures incorporated into the polymer matrix isdiscussed below along with commercial applications of the polymers.

In a non-limiting embodiment of the invention, a polyvinylacetal resinsuch as polyvinyl butyral (PVB) having indium tin oxide (ITO) orantimony tin oxide (ATO) nanostructures incorporated into the polymermatrix is formed. Such a polymer can be formed in the following manner.In the first step, a precursor solution for PVB is mixed with aprecursor for ITO or ATO nanostructures.

An example of a suitable precursor solution for PVB is polyvinyl alcohol(PVA). Suitable precursors for ITO nanostructures include monobutyl tintri-chloride and indium acetate. A suitable precursor for ATOnanostructures is antimony tri-chloride.

In the second step, ITO or ATO nanostructures are formed from theprecursor of the nanostructures in the polymer matrix. The nanostructureformation can be caused by adjusting the pH of the mixture followed byheating. The pH can be adjusted by introducing an agent, such asammonia, into the mixture. For ITO nanostructures in a PVA aqueoussolution, the nanostructures begin to form at a pH>8. After the pH isadjusted, the mixture is heated to a temperature of up to 200° C.Heating the solution to a temperature greater than 200° C. may cause thePVA matrix to decompose. As discussed above, heating the mixture for alonger time period can increase the size of the nanostructures.

The —OH groups on the PVA can attach to the nanostructures so the mainchain of the PVA molecule can stabilize the nanostructures via stericstabilization. By varying the degree of hydroxylation and the molecularweight of PVA, the stabilization effect of the PVA can be optimized.

In the third step, the precursor solution for the polymer is convertedto the polymer. As is well known in the art, the precursor solution canbe converted to PVB by adding PVA solution to the mixture and thenreacting the resulting mixture with butyraldehyde.

As discussed above, the properties of the final polymer can be effectedby factors such as the type and amount of ions formed during theprocess, the pressure at which the mixture is held, etc.

Typically, the final PVB polymer has an average molecular weight greaterthan 70,000 as measured by size exclusion chromatography using low anglelaser light scattering. On a weight basis, the final PVB polymertypically comprises 15 to 25% hydroxyl groups calculated as polyvinylalcohol (PVA); 0 to 10% residual ester groups calculated as polyvinylester, and the balance being acetal groups.

In a non-limiting embodiment of the invention, the final PVB polymer isused as an interlayer in a laminated glass transparency for automotiveand architectural applications. As is well known in the art, a laminatedglass transparency can be manufactured by interposing an interlayerbetween at least two transparent glass sheets.

In this particular embodiment of the invention, a laminated glasstransparency for an automotive and architectural applicationsembodiment, it is important that the nanostructures do not agglomerate.If the nanostructures were to agglomerate and effectively achieve adiameter of greater than 200 nm, the nanostructures would scattervisible light rays to such an extent that transmittance through theinterlayer would be insufficient for the application. A polymer withnanostructures having an acceptable size for the application, can bedetermined using a “haze value”. The haze value is associated with thedegree to which transparency is prevented. The larger the nanostructurespresent in the polymer matrix, the higher the haze value. According tothe present invention, laminated glass for automotive and architecturalapplications has a haze value of less than or equal to 1%, for example,less than or equal to 0.3%, or less than 0.2%, as measured using aHazeguard System from BYK-Gardner in Columbia, Md.

In another non-limiting embodiment of the invention, poly[bis(diethyleneglycol)diallylcarbonate] having oxide nanostructures such as titania,alumina, zirconia nanostructures incorporated into the polymer matrix isformed. Such a polymer can be formed in the following manner. In thefirst step, a precursor solution for poly[bis(diethyleneglycol)diallylcarbonate] is mixed with a precursor for titania, alumina,or zirconia nanostructures.

Suitable precursor solution for poly[bis(diethyleneglycol)diallylcarbonate] includes, but is not limited to, bis(diethyleneglycol)diallylcarbonate monomer. Suitable precursors for titaniananostructures include, but are not limited to, titanium iso-propoxide,titanium (IV) chloride and potassium titanyl oxalate. Suitableprecursors for alumina nanostructures include, but are not limited to,aluminum iso-propoxide, aluminum tri-tert-butoxide, aluminumtri-sec-butoxide, aluminum triethoxide, and aluminum pentanedionate.Suitable precursors for zirconia nanostructures include, but are notlimited to, zirconium iso-propoxide, zirconium tert-butoxide, zirconiumbutoxide, zirconium ethoxide, zirconium 2,4-pentanedionate, andzirconium trifluoropentane-dionate.

In the embodiment where a poly[bis(diethylene glycol)diallylcarbonate]is being formed having titania nanostructures incorporated into thepolymer matrix, the first step can comprise mixing titaniumiso-propoxide with a 1-10 wt % H₂O₂ solution and bis(diethyleneglycol)diallylcarbonate monomer. The H₂O₂ acts as an initiator fortitania nanostructures; particularly, titania nanostructures in theanatase form. Optionally, polymers such as polyoxyethylene (20) sorbitanmonooleate commercially available as Tween® 80 from ICI Ltd;(Bridgewater, N.J.) can be added to the solution to help stabilize thetitania nanostructures.

In the second step, the titania nanostructures are formed from theprecursor by heating the mixture to a temperature of up to 200° C.

In the third step, the precursor solution for the polymer is convertedinto bis(diethylene glycol)diallylcarbonate as is well known in the art.For example, isopropyl peroxycarbonate (IPP) which is a free radicalinitiator, can be added to bis(diethylene glycol)diallylcarbonatemonomer. The IPP can be dissolved directly into the monomer, poured intoa glass mold and heated above 70° C. for at least 8 hours or more toform poly[bis(diethylene glycol diallylcarbonate]. The IPP degrades intofree radicals that react with the allyl groups terminating the monomerto begin polymerization.

In a non-limiting embodiment of the invention, poly[bis(diethyleneglycol)diallylcarbonate] having titania, alumina, or zirconiananostructures incorporated into the matrix of the polymer can be usedas an optical lens. An optical lens made out of a poly[bis(diethyleneglycol)diallylcarbonate] formed according to the present invention willhave a larger elastic modulus and a higher refractive index than anoptical lens made out of standard poly[bis(diethyleneglycol)diallylcarbonate]. As a result of the higher refractive index, anoptical lens made out of polymer formed according to the presentinvention does not have to be as thick as a conventional optical lens tosatisfy a severe prescription.

A polymer with nanostructures having an acceptable size for theapplication can be determined using a “haze value”. According to thepresent invention, an optical lens has a haze value of less than orequal to 0.5%, for example 0.2%, as measured using a Hazeguard Systemfrom BYK Gardner.

In a non-limiting embodiment of the invention, a polyurethane having ITOor ATO nanostructures incorporated into the polymer matrix is formed.Such a polymer can be formed in the following manner. In the first step,a precursor solution for the trimethylol propane, methylenebis(4-cyclohexylisocyanate)thiodiethanol is mixed with a precursor forITO or ATO nanostructures.

A suitable precursor solution for the polyurethane is trimethylolpropane, methylene bis(4-cyclohexylisocyanate), thiodiethanol includes,but is not limited to, 1,4-butanediol. Suitable precursors for ITOnanostructures include monobutyl tin tri-chloride and indium acetate. Asuitable precursor for ATO nanostructures is antimony tri-chloride.

In the second step, ITO or ATO nanostructures are formed from theprecursor. The nanostructure formation can be caused by adjusting the pHof the solution by introducing an agent, such as ammonia, into themixture followed by heating the mixture. For ITO nanostructures, the ITOnanostructures start to form at pH>8. After the pH is adjusted, themixture is heated to a temperature of up to 200° C. As discussed above,heating the mixture for a longer time period can increase the size ofthe nanostructures.

In the third step, the 1,4-butanediol is mixed into trimethylol propane,methylene bis(4-cyclohexylisocyanate), thiodiethanol as is well known inthe art. For example, 1,4 butanediol, thiodiethanol, trimethylol propane(TMP), and Desmodur® W can all be mixed into a vessel and heated to 180°F. The mixture is mixed under vacuum for approximately 15 minutes, andthen a tin catalyst, such as dibutyltindilaurate or bismuth carboxylate,is added to the mixture in a 25 ppm concentration. The mixture is thencast into a glass mold and cured for at least 20 hours at 250° F. toform the polyurethane.

In a non-limiting embodiment, trimethylol propane, methylenebis(4-cyclohexylisocyanate), thiodiethanol having ITO or ATOnanostructures incorporated into the polymer matrix is used to form ananti-static coating for aircraft windows. The polymer with thenanostructures has an elastic modulus that is greater than that of thestandard trimethylol propane, methylenebis(4-cyclohexylisocyanate)thiodiethanol without ITO/ATO nanoparticles.

A polymer with nanostructures having an acceptable size for the aircraftwindow application can be determined using a “haze value”. According tothe present invention, a laminated aircraft window has a haze value ofless than or equal to 1%, for example 0.5%, as measured using aHazeguard System from BYK Gardner.

It will be readily appreciated by those skilled in the art thatmodifications may be made to the invention without departing from theconcepts disclosed in the foregoing description. Such modifications areto be considered as included within the scope of the invention.Accordingly, the particular embodiments described in detail hereinaboveare illustrative only and are not limiting as to the scope of theinvention, which is to be given the full breadth of the appended claimsand any and all equivalents thereof.

1. A method for making a polymer having a matrix that has nanostructuresincorporated into the matrix of the polymer, comprising: a. mixing aprecursor solution for the polymer of trimethylol propane, methylenebis(4-cyclohexylisocyanate), thiodiethanol with a precursor for thenanostructures selected from monobutyl tin tri-chloride and indiumacetate to form a mixture, wherein the mixture consists essentially ofthe precursor solution for the polymer and the precursor for thenanostructures; b. forming nanostructures in the mixture from theprecursor of the nanostructures wherein the nanostructures aresurrounded by the polymer precursor when they are formed; and c. forminga polymer from the precursor solution of the polymer so that thenanostructures are incorporated into the polymer matrix, wherein thenanostructures incorporated into the polymer matrix are in the range of1 nm to 1,000 nm in length.
 2. The method according to claim 1, whereinthe nanostructures are indium tin oxide.